This invention relates to metallic surgical implants, i.e., to metallic surgical construction elements which are intended to remain either permanently (endoprothesis) or only temporarily in human or animal bodies.
Implants of this type have been made completely ("Contimet" Titan Information, Ed. Hannover 1973) or partially (German Pat. No. 923,383) from metal. The drawback of these is the inadequate corrosion and stress-cracking resistance of the metals against the fluids and secretions of the living body as well as the insufficient abrasion resistance which results when parts of the implant slide relative to each other. The danger involved in metallic abrasion is that the abraded particles are carried into the surroundng tissues and become deposited therein. This may give rise to irritation and to the build up of connecting tissue which causes stiff joints. Also, the abrasion reduces the life expectency of the implant, so that repeated operations may be required, particularly with younger patients. Several metallic implants in the body or foreign bodies with different electrochemical potential may lead, via the body fluids and secretions, to the formation of electrochemical circuits in the body.
Metallic implants may be anchored to the bones by means of bone cements based on methyl methacrylate. This cement has a tendency to polymerize and to shrink, whereby the rigid seating of the implant becomes lost. Furthermore, over long periods, monomers are spread within the body and may produce toxicity and circulatory difficulties.
Implants made from solid oxide ceramic without (British Pat. No. 1,083,769) or with (German Pat. No. 583,589) a glossy transparent mineral glaze are also known. The implants are given the glaze to produce a glossy surface when they are used as anatomical or panoptical models, but not when they are used for surgical purposes. The drawback of oxide ceramic implants is their relatively great brittleness and low fracture elongation, which means that they must be relatively large. Accordingly, their application is excluded where insufficient space is available. Also, the notch sensitivity of these materials and the weight of implants manufactured therefrom are relatively high.